Salmonella spp. are members of the family Enterobacteriaceae. They are gram negative, facultatively anaerobic rods. Salmonella spp. are classified into serovars (serotypes) based on the lipopolysaccharide (O), flagellar protein (H), and sometimes the capsular (Vi) antigens.
Many of these Salmonella serovars have a broad host range and can infect a wide variety of animals, including mammals, birds, reptiles, amphibians, and insects. In addition, Salmonella can grow in plants and can survive in protozoa, soil, and water. Hence, reducing human infections will require the reduction of Salmonella in animals and limitation of transmission from the environment.
Salmonella are non-fastidious as they can multiply under various environmental conditions outside the living hosts. They do not require sodium chloride for growth, but can grow in the presence of 0.4 to 4%.
Salmonella is spread by the fecal-oral route and can be transmitted by
•food and water,
•by direct animal contact, and
•rarely from person-to-person.
When Salmonella bacteria are ingested, they pass through a person’s stomach and colonize the small and large intestine. There, the bacteria invade the intestinal mucosa and proliferate. The bacteria can invade the lymphoid tissues of the gastrointestinal tract and spread to the bloodstream
They are carried asymptomatically in the intestines or gall bladder of the person, and are continuously or intermittently shed in the feces. These bacteria are also shed in the feces of animals and humans that are ill. In addition, Salmonella spp. can be carried latently in the mesenteric lymph nodes or tonsils; these bacteria are not shed, but can become reactivated after stress or immunosuppression.
Salmonella gastroenteritis is characterized by the sudden onset of
• diarrhea (sometime blood-tinged),
• abdominal cramps
• fever, and
• occasionally nausea and vomiting
The gastro-intestinal tract of mammals (pigs and cattle) and birds (domestic poultry) is the principal reservoir of Salmonella spp. Some strains can also be found in other sources, such as cold-blooded animals (reptiles, turtles) and aquatic animals (molluscs, fish).
Transmission occurs when organisms, introduced into the kitchen in poultry carcasses, meat or unpasteurized milk, multiply in food owing to inadequate cooking, cross-contamination of cooked foods and inadequate storage. Person-to-person spread is common in institutions such as hospitals.
Transmission and infection of salmonella
